Enable Marketplace for Flipper (#3491)

Summary:
This is PR on top of: https://github.com/facebook/flipper/pull/3473

It adds an option to Settings to allow distribution of marketplace plugins.

Also includes a simple fetch function to retrieve data from external API/server.

## Changelog

Allow marketplace plugins

Pull Request resolved: https://github.com/facebook/flipper/pull/3491

Test Plan:
1. Enable marketplace
2. Provide custom marketplace server (it will serve the list of internal plugins with downloadURL)
3. Test if can see Available plugins and can download/remove the plugin
4. If new update for the plugin, it should also allow auto update

Reviewed By: antonk52

Differential Revision: D34586339

Pulled By: nikoant

fbshipit-source-id: c887982aa0f0f9abd3b5360f22e8692a2445d345

desktop/flipper-common/src/settings.tsx

@@ -39,6 +39,12 @@ export type Settings = {
   darkMode: 'dark' | 'light' | 'system';
   showWelcomeAtStartup: boolean;
   suppressPluginErrors: boolean;
+  /**
+   * Plugin marketplace - allow internal plugin distribution
+   */
+  enablePluginMarketplace: boolean;
+  marketplaceURL: string;
+  enablePluginMarketplaceAutoUpdate: boolean;
 };
 
 export enum ReleaseChannel {